Casein micelles: from the monomers to the supramolecular structure

Abstract The most relevant aspect concerning casein micelles lies in the fact that all the procedures employed in the transformation of milk into dairy products depend, directly or indirectly, on their stability or their controlled destabilization. Thus, the present paper aimed to present an updated review of the structural organization of casein micelles. Physicochemically, casein micelles can be defined as spherical, porous supramolecular aggregates, highly hydrated, negatively charged, with a mean diameter of about 200 nm, and presenting approximately 104polypeptide chains. Besides water, casein micelles are constituted of four types of casein molecule, namely αS1, αS2, β and κ-caseins, which are held together by means of hydrophobic and electrostatic interactions, and by the presence of minerals, mainly composed of calcium phosphate salts, which are considered the main factor responsible for maintaining the micellar structure. The stability of the casein micelles is attributed to the presence of an outer diffuse layer, basically composed of κ-casein. Although the colloidal properties of casein micelles are well known, there is still no consensus concerning their internal structure. Therefore, the main models describing the internal organization of casein micelles are presented in the final part of this article.摘要 与酪蛋白胶束（casein micelles）相关的最核心要点在于：所有将牛乳转化为乳制品的工艺，无论直接或间接，都依赖于其稳定性或可控去稳定化。因此，本文旨在对酪蛋白胶束的结构组织进行一次更新综述。从物理化学角度而言，酪蛋白胶束可被定义为球状、多孔的超分子聚集体，具有高度水合性与负电荷，平均直径约为200 nm，且包含约10^4条多肽链。除水之外，酪蛋白胶束由四种酪蛋白分子构成，即αS1、αS2、β与κ-酪蛋白，这些分子通过疏水作用、静电相互作用结合，并借助以磷酸钙盐为主要成分的矿物质维系结构，后者被认为是维持胶束结构的核心因素。酪蛋白胶束的稳定性源于其外部弥散层的存在，该层主要由κ-酪蛋白构成。尽管酪蛋白胶束的胶体特性已被广泛认知，但学界对于其内部结构尚未达成共识。因此，本文末尾将介绍几种用于描述酪蛋白胶束内部组织的主流模型。